This invention relates to torque transmitting devices and more particularly to such devices having fluid-operated pistons.
Prior art torque transmitting devices, such as clutches and brakes, generally provide a single piston which cooperates with a step diameter cylinder to establish separate operating annuli. One area of the piston is pressurized at initiation of engagement to provide take-up or clearance removal between the friction plates of the clutch or brake. The other piston area is fed generally through an orifice so that the total piston area is pressurized for complete clutch engagement. In these prior art devices, the entire operating piston must move against the return spring to achieve clearance removal. The time required to fill the cylinder and establish the pressure to achieve this piston movement can vary considerably from device to device and also can extend over a time period of 100 milliseconds or longer.